(1) Field of the Invention
The present invention relates generally to methods and apparatus for distribution of information, more specifically to electronically displaying informational content and, more particularly to a reusable, high contrast, very high resolution, rewritable print medium and methods for fabrication thereof.
(2) Description of the Related Art
Hard copy and, more recently, electronic display information is communicated in many forms and by many means. Erasable-rewritable print media communication tools range from simple pencil-on-paper to chalk-on-blackboard to dry marker pen-on-whiteboard. More sophisticated hard copy processes allow mechanized business and commercial printing processes—including laser and ink-jet printers, offset lithography, silkscreen, and the like, for printing—but those processes are usually restricted to the permanent print category (versus “erasable print” or “erasably writable” formats and methods). The bulk of print is commercially produced and made available through books, magazines, newspapers, and various other forms of permanent ink (“toner” or, more generically “colorant”) on cellulose fiber media (commonly known as “paper”). The information content—generally alphanumeric text and graphical images—contained in this form is of a sufficiently high resolution and contrast to be easily read over prolonged periods of time without eye discomfort. Compared to electronic devices, hard copy media has the advantages of having zero power consumption while remaining highly portable, allowing comfortable reading in locations of choice and body positions that may be periodically varied to change reading distance and posture to maintain comfort. Such print media, however, requires a relatively high cost in printing, binding, warehousing, and distribution. The hard copy cost, independent of printing means, is normally amortized through a single reading, after which the book or other document is physically stored or discarded. Since these latter cost factors also require a definable time expenditure between content generation and availability to the reader, the content of the media is not contemporaneous; e.g., today's newspaper actually is filled with “what happened yesterday.”
Much print is created by hand, e.g., using pen or pencil on paper. In many cases, such print is used for temporary information storage such as phone numbers, reminders, grocery lists, and appointments. Print media for such print commonly consists of notepads, Post-It® notes, calendars, tear-sheet display boards, and the like. In each instance, the medium is usually used for its intended purpose then later discarded or ignored, leading to waste, recycling costs, and clutter.
Chalk-on-chalkboard and dry marker pen-on-whiteboard print overcome issues of media waste and clutter. Such print images are produced with powders or inks that coat the media surface without permanent attachment, allowing easy image viewing, erasing, and subsequent re-imaging. However, such print is not applicable to portable media applications, such as grocery lists, bound image applications, or other uses in which the media surface may be smeared by contact. A further disadvantage is the messy residue that results from the removal of the chalk or ink from the media surface.
Business printers, such as the ubiquitous laser and ink-jet printers, in connection with the Internet overcome some of these problems and provide contemporaneous information distribution with an attendant hard copy printing availability, but at a higher cost per page and usually at a lower quality or in a different format than commercial print. (The term Internet is used herein as a generic term for a collection of distributed, interconnected networks (ARPANET, DARPANET, World Wide Web, or the like) that are linked together by a set of industry standard protocols (e.g., TCP/IP, HTTP, UDP, and the like) to form a generally global, distributed network. (Private and proprietary intranets are also known and are amenable to conforming uses of the present invention.)
Computers, on the other hand, provide virtually instantaneous distribution of content through the Internet at significantly reduced cost to the reader. Similarly, with the advent of handheld devices such as palmtop computers, electronic books, net-ready telephones, and “personal digital assistants” (PDAs), print can be generated on electronic displays of varying sizes and types. Computer displays, however, provide far less comfortable readability by displaying content at significantly lower resolution than hard copy media. Cathode ray tube (“CRT”) displays have greater resolution capability but have low portability, if any, and require substantially stationary body positioning and reading at a somewhat fixed focal length, leading to comparatively rapid eye strain and posture discomfort. Liquid crystal displays (“LCD”) generally used in portable computers allow somewhat greater portability, but at the expense of display contrast, off-axis viewability, and higher cost. In part, the lower resolution of portable displays stems from the difficulty of matrix addressing at higher resolution.
FIG. 1AA (Prior Art) exemplifies the basic operation of a flat panel electronic display, such as a commercially available, flat panel, LCD 1 (dashed lines are used in this drawing to indicate continuation of discrete elements of the apparatus so as to make the drawing less complicated). Basically, the LCD 1 includes a plurality of picture elements (“pixels”) defining the resolution of the display, generally formed by an array of thin film transistors (“TFT”) and too small to be seen in this FIGURE (e.g., 600 dots per inch (“dpi”). A plurality of gate lines 2 and data lines 3 form a pixel control grid for active area “B” of the panel 1. The gate lines 2 and data lines 3 extend as leads 5 outside of the active area B for connection to known manner integrated circuit drivers. A plurality of pads, one for each line, are formed in region “C” about the periphery of the active area B as discrete pad regions 4 are coupled by the leads 5 to the gate and data lines 2, 3. Color LCD is produced by backlighting the individually switched pixels crystals through color filters. Note importantly that the resolution of the screen is limited by the technology related to interconnect wiring—namely, between the gate and data lines and the microprocessor or memory sending data—and driver size for each pixel. Moreover, such a device requires power to maintain each pixel in its current state and continually to backlight the crystal screen.
The at least one order of magnitude lower resolution of computer displays in comparison to commercial hard copy commonly prevents the reader from seeing a full-page comparable document at one time. Moreover, because of screen size constraints, without a very large video monitor or shrinking the page to fit a screen, the reader must use manual controls to scroll the displayed image down the document page in order to read its entire content. Furthermore, graphic images often can not fit on a single screen without severe zoom-out reduction in size, limiting the detail which can be displayed. Still further, there is the requirement of booting-up the computing device, turning on the specific application (notepad, calendar, or the like), and making at least one user command entry to obtain a document page of interest. More often than not, rather than using a PDA to make a note, a simple note scribbled on a piece of paper is much more convenient.
In addition to the aforementioned shortcomings of electronic displays, such displays are relatively high in power consumption, particularly if the screen is of the active transistor type. Also, they suffer from relatively poor contrast (viewability) in outdoor or other bright ambient environment conditions. Emissive displays, such as CRT, plasma, light emitting diode (“LED”), and backlit LCD, have self-illuminated picture elements (“pixels”). Emissive displays have excessive power consumption by virtue of the need to produce light. Such self-illumination is still comparatively low in brightness and therefore appears dark in bright ambient viewing conditions due to the eye's automatic adaptation to the ambient brightness. Non-backlit LCDs have poor contrast under virtually all ambient illumination; the ambient light reflected from each LCD pixel must pass through polarizers that significantly reduce pixel brightness relative to ambient brightness. This makes the LCD appear dark and of poor contrast. Prior art electronic displays used in computers and televisions have therefore been limited to practical use under controlled office and home ambient illumination. With the advent of mobile computer appliances, such as web-based telephones, palmtop computers, and televisions, there is a growing need for display technologies that provide good viewability under the wider range of ambient illumination conditions in which users commonly communicate, do business and are entertained. Mobile appliances demand low power consumption for long battery life. Therefore, there is a growing need for an alternative to conventional electronic displays that consume less power.
When a long document is downloaded from the Internet, the reader will commonly print the contents to gain back the aforementioned hard copy media benefits. Such printing, however, adds local cost to the process for documents that commonly are still read just once and eventually discarded. The recycling of paper barely makes a dent in the multiple costs to the environment. For information distribution, current computer solutions are, thereby, still somewhat antithetical to the needs for distribution of books, periodicals such as magazines and newspapers, and the like.
Electrostatically polarized, bichromal particles for displays have been known since the early 1960's. The need for an electronic paper-like print means has recently prompted development of at least two electrochromic picture element (pixel) colorants: (1) a microencapsulated electrophoretic colorant (see e.g., U.S. Pat. No. 6,124,851 (Jacobson) for an ELECTRONIC BOOK WITH MULTIPLE PAGE DISPLAYS, E Ink Corp., assignee), and (2) a field rotatable bichromal colorant sphere (e.g., the Xerox® Gyricon™). Each of these electrochromic colorants is approximately hemispherically bichromal, where one hemisphere of each microcapsule is made the display background color (e.g., white) while the second hemisphere is made the print or image color (e.g., black or dark blue). The colorants are field translated or rotated so the desired hemisphere color faces the observer at each pixel. FIGS. 1BB and 1CC schematically depict this type of prior art.
Electronic ink is a recent development. E Ink Corporation (Cambridge, Mass.; www.eink.com) provides an electronic ink in a liquid form that can be coated onto a surface. Within the coating are tiny microcapsules (e.g., about 30 μm to 100 μm in diameter, viz. about as thick as a human hair, thus quite visible to the naked eye). As illustrated in FIG. 1BB (Prior Art), each microcapsule 6 has white particles 7 suspended in a dark dye 8. When an electric field is applied and sustained in a first polarity, the white particles move to one end of the microcapsule where they become visible; this makes the surface appear white at that spot. A carrier 9 is provided. An opposite polarity electric field pulls the particles to the other end of the microcapsules where they are substantially hidden by the dye; this makes the surface appear dark at that spot.
The Xerox Gyricon sphere is described in certain patents. FIG. 1CC (Prior Art) is a schematic illustration of this type of sphere. U.S. Pat. No. 4,126,854 (Sheridon '854) describes a bichromal sphere having colored hemispheres of differing Zeta potential that allow the spheres to rotate in a dielectric fluid under influence of an addressable electrical field. U.S. Pat. No. 4,143,103 (Sheridon '103) describes a display system using bichromal spheres in a transparent polymeric material. U.S. Pat. No. 5,604,027 (Sheridon '027), issued Feb. 18, 1997, for SOME USES OF MICROENCAPSULATION FOR ELECTRIC PAPER, describes a printer. Essentially, each sphere 10 (again, about 30 μm in diameter) has a bichromal ball 13 having two hemispheres 11, 12, typically one black and one white, each having different electrical properties. Each ball is enclosed within a spherical shell 14 and a space 15 between the ball and shell is filled with a liquid to form a microsphere so that the ball is free to rotate in response to an electrical field. The microspheres can be mixed into a substrate which can be formed into sheets or can be applied to a surface. The result is a film which can form an image from an applied and sustained electrical field. Currently, picture element (“pixel”) resolution using this Gyricon spheres is limited to about 100 dpi.
Thus, in the known prior art, each individual colorant device is roughly hemispherically bichromal; one hemisphere is made the display background color (e.g. white) while the second hemisphere is made the print or image color (e.g. black or dark blue). In accordance with the text and image data, these microsphere-based colorant devices are field translated or rotated so the desired hemisphere color faces the observer at each respective pixel. It can be noted that, in commercial practice, displays made from these colorants have relatively poor contrast and color. The layer containing the microcapsules is generally at least 3 or 4 microcapsules thick. Light that penetrates beyond the layer surface internally reflects off the backside hemispheres causing color (e.g. black and white) intermixing. The image is, for example, thus rendered dark gray against a light gray background. Thus, these technologies do not provide a promising extendability and scaling to high resolution color displays because the colorant switches only between two opaque colors, disallowing passage of light from different colorant layers for a given pixel. Still further, as is these colorant technologies produce a visually poor display resolution relative to hard copy print due to the relatively large size of the colorant microcapsule spheres. Moreover, the spheres are bichromal, limiting application to two-color rather than true full color display. Further still, the need for overlapping spheres in multiple layers to achieve adequate color density limits pixel resolution Yet another limitation is that these colorant technologies suffer from poor pixel switching times in comparison to standard CRT and LCD technology. Each technology relies on the electrophoretic movement of colorant mass in a dielectric material, such as isoparafin. The color rotation speed of dichroic spheres under practical electrical field intensities is in the range of 20 milliseconds (ms) or more. At that rate, a 300 dpi resolution printer employing an electrode array would be limited to under one page per minute print speed. These large sphere colorants require high switching voltages (e.g. 80-200 volts) to obtain adequate fields through the consequently thick (>100 μm) carrier-colorant layer. Such switching voltages add high cost to the pixel drive electronics, similar to that of the high-end matrix LCD apparatus. Thus, those involved in the development of microcapsule type colorants are struggling with the resolution of these and other related problems rather than focusing on a new molecular level technology as described in accordance with the present invention.
There are limitations to microcapsule technologies. The Gyricon microcapsule technology produces limited resolution compared to hard copy due to the relatively large size of the microcapsule spheres, typically a diameter greater than 30 μm. As schematically illustrated in FIG. 1DD (Prior Art), overlapping spheres in multiple layers are needed to achieve adequate color density, limiting pixel resolution to the order of 300-400 dots-per-inch (“dpi”), whereas, depending on the viewing conditions, the unaided human eye can discriminate to over 1000 dpi. Displays made from microcapsules tend to have poor contrast and color because light that penetrates beyond the surface layer of microcapsules reflects back off subjacent microcapsules causing color intermixing. As also demonstrated in FIG. 1DD, poor image contrast arises from backside reflections from each microcapsule. Light entering and penetrating the interstices of a first layer of microcapsules (now illustrated as hemispherically colored black and white circles 8) in the media surface coating 16 reflects and is absorbed by the backside, as well as front side, hemispheres of subsequent microcapsule layers. Low color density areas of the image become darker and high color density areas become lighter than would otherwise occur if the microcapsules were of uniform color throughout their exterior (as is true with pigments, and dyes used in standard printing processes). Thus, in a device using layers of bichromal microcapsules, the image is often actually rendered dark gray against a light gray background
Another limitation to achieving high contrast is that the microcapsules of the type shown in FIG. 1BB superimposes the two encapsulated components so that independently of which colorant faces the observer, the second colorant is also visible. Because of the finite nature of the white particles 7 and dark color dye 8, when the white hemisphere is displayed (rotated toward the viewer), dye will still show in the interstitial spaces between the white particles; likewise, when the dye hemisphere is displayed, the inherent transparent nature of the dye allows reflection toward the viewer off the subjacent white particles, lightening the dye color (e.g., deep blue to a medium blue). In other words, neither one hundred percent reflection of white nor one hundred percent of absorption is achieved. Of the type of microcapsule as illustrated in FIG. 1CC, while the hemispheres are opaque black and opaque white, respectively, when light hits the ball 13 it also goes between the spheres 10 similarly to as shown in FIG. 1DD, again limiting contrast and resolution capability.
Furthermore, because they rely upon the electrophoretic movement of a mass in a liquid, these microcapsule technologies suffer from poor pixel switching times in comparison to standard CRT and LCD screens. Color switching comprises the relative rotational or translational movement of solid particles and liquid from the forward facing to backside facing hemispheres. Relatively slow color switching time is the simple result of the microcapsule's mass and fluidic drag within the sphere. The combined mass and fluidic drag define the time required to affect a color switch at a given pixel. This, in turn, defines both the switching energy requirements and the imaging speed, or “throughput,” of a printer using media with this technology.
Further still, these relatively large microcapsules require high switching voltages (e.g., 20-200 volts) to obtain adequate fields through the relatively thick (greater than 100 μm), multiple microcapsule layers 16. Such switching voltages add further cost to the pixel drive electronics, making it comparable to the cost of an LCD screen.
Still further, these microcapsule technologies do not provide a promising extension to high resolution color displays because the colorant switches only between two opaque colors, disallowing passage of light from different colorant subjacent layers for a given pixel. In other words, microcapsule colorant is not a true dye where outside the particular dye absorption bandwidth the colorant becomes transparent, allowing different layered chemical compositions to render full color images (e.g., as used in color film and print technology). Thus, to gain a full color adaptation, microcapsule colorant based devices will be limited to mosaic patterning which further limits resolution and, ultimately, print quality.
Moreover, the microcapsules themselves suffer from difficult manufacturing processes and relatively poor durability. Microcapsules, by their nature, have thin walls that are subject to breakage with subsequent liquid leakage that destroys colorant functionality. Wall thickness is typically of the order of 1-2 μm (or about 10% of diameter). Microcapsule breakage may occur by pressure externally applied to the media surface, media folding, and by the coating process itself used to make the media. This limits the ability of the display media to be folded or even contacted without a high probability of capsule breakage and subsequent loss of imaging function.
It can be concluded that there is not a currently available electronic information-displaying mechanism which does not have at least some of the foregoing described limitations. More particularly with respect to the present invention, among the collection of present print and display state-of-the-art technologies there does not exist a rewritable media capable of commercial hard copy resolution, contrast, and durability. Further, there is not a rewritable media that has the full color quality appearance nor print readability of commercially printed paper. Thus, there is a need for new and improved print media.
Still further, there is not an electronic rewritable media having good bright ambient illumination viewability and low power consumption.
Still further in the state-of-the-art, for digital data, mass storage media is another form of “rewritable media.” Conventional mass storage media includes disks and tapes having a magnetic surface coating. The surface coating used in disks and tapes generally contains a thin film deposition, or polymer suspension, ferromagnetic crystal layer. When exposed to an externally applied magnetic field, the ferromagnetic crystals develop a residual magnetic field that remains stable in the absence of the external field. The surface coating is written for data storage by a magnetic writing head translated (by disk revolving or tape streaming) relative to the surface coating. Data is stored in the form of patterns of residual magnetic fields over the surface. The data is retrieved by a magnetic read head (e.g., an electric coil) translated relative to the encoded coating surface, transforming the residual magnetic field patterns into an oscillating electrical current stream representing the original electronic data form. The area density and field strength of the magnetically recorded data is determined by the size of the ferromagnetic crystal domains. In an alternate form, digital data is stored on CD-ROM media in the form of a pattern of laser-ablated or impressed pits on the surface of a light reflective disk. The data is read optically as the disk rotates by reflecting light off the surface into a light sensor. The sensed signal changes as it alternately strikes pits and reflective regions between successive pits. The density of data storage on the disk is a function of the size of the ablated pits and intervening reflective regions. In general, data can be read from a CD-ROM at a significantly greater rate than data can be written, since writing requires physical ablation of material in making pits. However, at present, writable CD technology is in its infancy and quality apparatus is relatively expensive.
With the ever-increasing need to store more data on storage media, there is increasing need for rewritable storage data storage elements that are much smaller than available through conventional magnetic and CD-ROM media, creating a higher data density capability. There is also a need to write data at higher data rates.
There is a need for a new technology for the field of displaying information that is adaptable to a wide range of implementations. Molecular science holds the promise for solution to many, if not all, of the shortcomings of the conventional methods and apparatus currently available for erasable writing and data storage, retrieval and display. Thus, the present invention provides molecular level solutions, viz., molecular systems in the form of molecular level optical switches, that can be assembled easily to make displays, electronic books, rewritable media, electronic lenses, electrically-controlled tinting for windows and mirrors, optical crossbar switches for fiber optic communications, and much more.
Due to the nature of the present invention which reaches into molecular science technology, it will become apparent to the reader that there also arises a question as to what is “print media” and what is a “writing surface” and what is a “display screen” (more simply “display” or “screen” as best fits the context). In some implementations, discriminating as to which conventional definition such an apparatus or method of use falls into may be less than clear. Therefore, it should be noted that no limitation on the scope of the present invention is intended by the use of such a particular conventional term when describing the details and no such limitation should be implied therefrom. Thus, further limitations regarding convention displays is appropriate to understanding the need for and objects and advantages of the present invention.